This invention relates generally to aiming and pointing systems for ground based weapons equipment and, particularly, to a system of the type described using a north finding system. More particularly, this invention relates to a system which provides operating personnel with the pointing angles of a weapon relative to north and local horizontal and relative to a target.
Prior art systems for the purposes described feature a gyrocompassing device using a conventional spinning wheel two axis gyroscope (gyro) to find the pointing angle of the weapon relative to north. The angle is then transferred optically to a fixed standard called an aiming circle. The device is removed from the weapon before firing. All corrections for angular errors caused by firing are subsequently removed by optically re-aligning the weapon to the aiming circle.
Gyrocompassing devices are known which feature a stabilized reference package. An arrangement of this type includes a precision gyro that is maintained in the horizontal position by isolating the gyro from the weapon on a stabilized platform. This technology is necessarily cumbersome and expensive because it requires mechanism including at least three gyroscopes, two level sensing devices and three gimbals.
Strapped down ring laser gyro packages are also known. Again, this technology is more cumbersome and more expensive than otherwise desired because it must include three ring laser gyros and three accelerometers, as will be appreciated by those skilled in the art.
The aforementioned prior art arrangements present several problems that need to be solved. For example, the weapon must be leveled to within 0.25 degrees from the horizontal in order to gyrocompass. Spinning wheel gyroscopes have degraded accuracies when gyrocompassing at tilts due to mass unbalance error terms and characteristics. Even when leveled, such arrangements are only marginally accurate for long range projectiles. Typical accuracy is five mils (one sigma).
Further, spinning wheel systems cannot be permanently affixed to the weapon during transportation or firing because the vibration and shock which ensues reduces system reliability. Consequently, these systems only obtain the initial pointing angle of the weapon and are not usable to provide continuous pointing data while the weapon is being aimed or after firing. Also, mounting and dismounting these systems is, at best, inefficient and even dangerous during weapon firing conditions.
Also, relying on the aforementioned optical transferring of the pointing angle to an aiming circle prevents using current optical technologies when obscuring conditions, such as rain, snow, smoke, or other environmental abnormalities, occur. Also, optical transfer techniques are time consuming and are subject to human error.
Technologies using three gyros, require that the gyros be sufficiently accurate to use for the purposes intended and hence, are too expensive for practical application.
The present invention overcomes these problems and has several other significant advantages. For example, with the arrangement to be herein described, gyrocompassing can be performed for any weapon pointing elevation up to twenty-five degrees from the horizontal because the gyro used, which is preferably a ring laser gyro, or any other type gyro unaffected by mass unbalance error characteristics, is insensitive to tilts. No time is required to level the weapon for gyrocompassing, and after gyrocompassing the system will continue to measure the weapon pointing angles for any weapon attitude. Further, the accuracy of the system described herein has been found to be equal or less than one mil under military environmental conditions.
Also, the present system can be permanently affixed to the weapon. It is inherently rugged in design and is tolerant to shock and vibration. Therefore, constant updates of the weapon pointing angles are provided while the weapon is being slewed to the target direction.
A particular feature of the invention is that it contains its own displays to indicate aiming angles so as to be useful under a variety of otherwise interfering environmental conditions. Additionally, the system can be used to re-align the weapon immediately after firing without any auxiliary equipment.
Further, the present invention enables the performance requirements to be met by using a single gyro and two accelerometers as sensors. Thus, the design is more economical when compared to systems for the purposes described now known in the art.